1. Field of Invention
The present invention relates to a method of resolving photoelectron coupling. More particularly, the present invention relates to a method of resolving photoelectron coupling resulting from the operation of a staggered charge-coupled device inside a scanner.
2. Description of Related Art
The optical sensors used by scanners can be divided into linear optical sensors such as linear charge-coupled device (linear CCD) or subsequently developed staggered optical sensors such as staggered charge-coupled device (staggered CCD).
FIG. 1 is a schematic diagram showing the layout of a conventional staggered charge-coupled device. As shown in FIG. 1, each group of optical sensors in the staggered CCD includes a pair of linear optical sensor arrays, often referred to as an odd optical sensor array and an even optical sensor array. These two rows of optical sensor arrays have a line separation of M pixels. Since a color scanner needs to process the three primary colors, namely, red (R), green (G) and blue (B), there are three sets of optical sensor groups. Because the effect and method of operation for each optical sensor group are identical, the operation of only one of the optical sensor groupsxe2x80x94the one for processing red color, is selected in the following illustration.
When an even optical sensor array 124 processes the nth row of pixels of a document 100, the even pixels such as 2, 4, 6 and 8 are extracted. Similarly, when the odd optical sensor array 122 processes the nth row of pixels, the odd pixels such as 1, 3, 5 and 7 are extracted. After the odd optical sensor array 122 has finished extracting the nth row of pixels, a processing circuit 146 outputs the extracted pixels of the two rows of optical sensor arrays in sequence. Ultimately, the nth row of pixel data is output as a data series 102 for processing by a later stage circuit.
However, as the odd optical sensor array 122 processes the nth row of pixels of the document 100 and because the odd and the even optical sensor arrays have a line separation of M pixels, the even optical sensor array 124 will scan the (n+M)th row of pixels. If a scan document (the document 100 in FIG. 1) has darker and lighter regions as shown in FIG. 1, the even optical sensor array 124 and the odd optical sensor array 122 will capture the (n+M)th row and the nth row of pixels during a scanning period t. Since the even optical sensor array 124 scans a strip of the document in the lighter region, the number of photoelectrons absorbed is larger. Because of this, the odd optical sensor array 122 scanning the darker region of the document may absorb some of the photoelectrons captured by the even optical sensor array 124 and lead to a whitening of the darker region. In other words, the original black color region becomes a gray color region and hence the scanning operation produces undesirable image distortions. Using the data series 102 as an example, the sequential output pixel data will result in alternating gray, black, gray, black . . . instead of a uniform blackness with the identical brightness level of the original image.
On the other hand, because a portion of the image captured by the even optical sensor array 124 is lost to the odd optical sensor array 122, the colors of the (n+M)th row of pixels captured by the even optical sensor array 124 may also be distorted.
Hence, the two rows of optical sensor arrays affect each other leading to a partial coupling of the photoelectrons captured by the odd optical sensor array 122 and the photoelectrons captured by the even optical sensor array 124. Unless the staggered CCD of a scanner is modified in some ways, color distortion is bound to be present.
Conventionally, the only method of resolving the coupling in a staggered CCD is to average out the first pixel brightness value and the second pixel brightness value of the data series 102. In other words, the brightness value of the even pixel and the odd pixel are averaged to produce the color brightness value of the nth row of pixels.
However, with this type of averaging, true color of the original color is hidden. In effect, the arrangement lowers the genuine color brightness level of even pixels and raises the genuine color brightness level of the odd pixels.
Accordingly, one object of the present invention is to provide a method of resolving photoelectron coupling resulting from operating a staggered charge-coupled device inside a scanner so that color distortion is minimized. In addition, this method also provides an effect means of calibrating color brightness level.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a method of resolving photoelectron coupling of a staggered charge-coupled device. During a scanning period t, the amount of photoelectrons transferred between the batch of photoelectrons captured by exposing an optical sensor array and the batch of photoelectrons captured by exposing a neighboring optical sensor array is measured. Thereafter, the amount of transferred photoelectrons is subtracted from the batch of photoelectrons captured by exposing the optical sensor to find a more accurate number of photoelectrons captured by the optical sensor in the period t for use as the brightness value.
Through a relatively simple computation, additional photoelectrons from a neighboring optical sensor array captured by the optical sensor array or photoelectrons originally captured by the optical sensor array but transferred to the neighboring optical sensor array can be found so that a correct brightness value for an image is always secured.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.